1. Field of the Invention
The present invention relates to a vane pump having volume variable pump chambers communicatable with an inlet and an outlet.
2. Description of Related Art
FIGS. 20–22 show a previously proposed vane pump 100. The vane pump 100 includes a ring 130, which is interposed between first and second plates 110, 120. A rotor chamber is defined radially inward of the ring 130. A rotor 150, which supports a plurality of radially reciprocable vanes 140, is rotatably supported in the rotor chamber in such a manner that a rotational axis of the rotor 150 is displaced from the center of the rotor chamber. A plurality of volume variable pump chambers 160 is defined by the vanes 140 between an inner peripheral wall surface of the ring 130 and an outer peripheral wall surface of the rotor 150. A volume of each pump chamber 160 changes when the rotor 150 is rotated.
When the rotational axis of the rotor 150 is oriented in the vertical direction (a top-bottom direction in FIG. 20) in a manner shown in FIG. 20, the second plate 120 is placed below the ring 130. The second plate 120 includes an inlet 180 and an outlet 200. The inlet 180 is communicated with a corresponding one of the pump chambers 160 through an intake groove 170 recessed in the second plate 120, and the outlet 200 is communicated with a corresponding one of the pump chambers 160 through a discharge groove 190 recessed in the second plate 120.
The intake groove 170 is provided in a volume increasing region where the volume of each corresponding pump chamber 160 increases when the rotor 150 is rotated. The intake groove 170 is shaped into an arcuate shape, which extends along the inner peripheral wall surface of the ring 130.
The discharge groove 190 is provided in a volume decreasing region where the volume of each corresponding pump chamber 160 decreases when the rotor 150 is rotated. Similar to the intake groove 170, the discharge groove 190 is shaped into an arcuate shape, which extends along the inner peripheral wall surface of the ring 130.
In the previously proposed vane pump 100, abrasive debris or abrasive particles are generated through sliding movement of the vanes 140 along the ring 130 and the plates 110, 120 when the rotor 150 is rotated. A majority of the abrasive particles is discharged through the outlet 200 along with the working fluid. However, as shown in FIG. 22, a fraction of the abrasive particles is accumulated in an end of the discharge groove 190, which extends from the outlet 200 in the rotational direction (a left direction in FIG. 22) of the rotor 150. Thus, when the amount of accumulated abrasive particles is increased, a portion of the accumulated abrasive particles enters an operational range of the vanes 140 beyond the discharge groove 190 and is thus scraped by the rotating vanes 140. As a result, the abrasive particles are introduced into a sliding component clearance (e.g., a clearance between the plate 120 and each vane 140), causing locking of the rotating vane pump 100.
Particularly, in a case of a pump having a small discharge rate or volume (e.g., a pump used for evaporant leakage check or vapor leakage check), a drive torque of the motor, which rotates the rotor 150, is relatively small. Thus, such a pump can be easily locked by the abrasive particles entered into the sliding component clearance. Therefore, discharge of the abrasive particles from the pump need to be performed in a reliable manner.